In semiconductor manufacturing facilities or chemical related facilities, a pressure type flow rate control apparatus FCS and a thermal type mass flow rate control apparatus MFC are widely employed, in general, to control the flow rate of a fluid supply line. The afore-mentioned pressure type flow rate control apparatus FCS is equipped with a pressure sensor to detect fluid pressure on the upstream side and/or the downstream side from a throttle mechanism, such as a sonic nozzle, an orifice, and the like, and a means to display all the pressure detected to the outside is provided so that pressure at every part of the fluid supply line can be easily sensed with the aid thereof even at a time when fluid is not actually flowing through the pressure type flow rate control apparatus FCS.
On the other hand, it is difficult to sense the pressure of each part of the gas supply line using the afore-mentioned thermal type mass flow rate control apparatus MFC, and it is also difficult to display to the outside the pressure detected as the pressure type flow rate control apparatus FCS can do because the pressure type flow rate control apparatus FCS and the thermal type mass flow rate control apparatus MFC are basically different in operating mechanism as pressure sensors (its function to detect pressure).
FIG. 13 illustrates a basic circuit diagram for flow rate control of a fluid supply line by means of a flow rate control apparatus D consisting of the afore-mentioned pressure type flow rate control apparatus FCS or the thermal type mass flow rate control apparatus MFC, wherein the fluid to be controlled is a gas. Referring to FIG. 13, a purge gas supply line B and a process gas supply line A are connected in parallel on the upstream side from the flow rate control apparatus D, wherein the flow rate control apparatus D consists of a pressure type flow rate control apparatus FCS or a thermal type mass flow rate control apparatus MFC, and a process gas use line C is connected downstream from the flow rate control apparatus D. Furthermore, the afore-mentioned gas supply lines A, B and gas use line C are equipped with valves V1, V2, and V3, respectively.
On the other hand, for the fluid supply line shown in FIG. 13, it is common practice to conduct an inspection regularly to see how valves V1 to V3 are functioning. This regular check is a necessity to ensure a stable supply of the required process gas to prescribed parts through the process gas use line C.
Specifically, the inspection (hereinafter called a “check”) of the afore-mentioned valves V1 to V3 normally includes a check on how the valves are operating (including the operation of a valve actuator) and another check on the sheet leak of the valves. However, in the case wherein a thermal type mass flow rate control apparatus MFC is employed in the flow rate control apparatus D, it is not possible, for example, to detect a sheet leak of the valve V3 from the detected value obtained by detecting changes of the gas pressure of the process gas use line C using the thermal type mass flow rate control apparatus MFC.
As a result, to perform a sheet leak check of valve V3 of the process gas use line C, it is necessary to remove valve V3 from the pipe and to conduct the check using a separately provided test device, which makes the sheet leak check of valve V3 troublesome and time-consuming. The same issues apply to valves V1 and V2 on the upstream side from the flow rate control apparatus D. Normally, sheet leak of these valves V1, V2 is checked by removing them from the pipe and placing them on a sheet leak testing device that is separately provided, thus making the sheet leak check of valves V1, V2 troublesome and time-consuming as well.    [Patent Document 1] Japanese Unexamined Patent Application Publication No 8-338546    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2000-66732    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2000-322130    [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2003-195948    [Patent Document 5] Japanese Unexamined Patent Application Publication No. 2004-199109